Asphalt paving compositions, which include a mixture of asphalt binder and aggregate, have long been employed in the manufacture of pavements. The long-standing technological challenge with these pavements has been their behavior at extreme temperatures. That is, at high temperatures, the pavements become soft; and at low temperatures, the pavements are brittle.
For decades, additives have been employed to alleviate the problems experienced at extreme temperatures. For example, polymers have been added to asphalt binder compositions. U.S. Pat. No. 4,145,322 teaches polymer-modified bitumen compositions that include elastomers (e.g., polyisoprene, butyl rubber, SBR rubber) that can be employed to improve the mechanical properties of, the bitumens, especially the elastomeric properties. And, the use of particular block copolymers of styrene and diene monomer in these bitumen compositions provides compositions having desirable mechanical properties even at low temperatures.
In a similar fashion, JP 51-149312 (1976) teaches modified asphalt compositions that include a phosphorus compound, such as phosphorus pentoxide, polyphosphoric acid, or thionating agents. It is suggested that these phosphorus compounds can modify the asphalt because they bond to the asphaltene in the asphalt to further strengthen the gel structure. In order to overcome dispersibility and handling issues associated with these phosphorus compounds, the phosphorus compounds are mixed with petroleum compositions, and the mixture is added to the asphalt composition. The petroleum compositions are characterized by an ignition point of 150° C. or higher and include 0.5-40% asphaltenes. The phosphorus compounds can be included in the petroleum composition in an amount from 0.5 to 50 weight percent, and the amount of phosphorus compound added to the asphalt to be modified may be from 0.2 to 5.0 weight percent.
U.S. Pat. No. 6,569,351 teaches polymer modified asphalt compositions prepared by combining an accelerator-gel additive with polymer and asphalt, and curing the polymer-modified asphalt at a temperature between 200° F. and 500° F. The accelerator-gel additives include 2-75% accelerator, 25-88% processing oil, and 0.5-10% clay. The accelerator may include sulfur, 4,4′-dithiodimorpholine, thiazole derivatives, dithiocarbanates, thionating agents, phosphorus pentoxide, zinc stearate, ammonium stearate, sodium hydroxide, potassium hydroxide, calcium hydroxide, aluminum oxide, or combinations of these or other vulcanizers or accelerators. The accelerator-gel additive may be added to concentrates between approximately 1-25% polymer.
U.S. Pat. No. 5,990,206 teaches a mixture of polymer and phosphorus compound (modifier composition) for use in asphalt compositions. The polymer may include a rubber-base polymers (modifier) and/or a resin-based polymer (modifier). The phosphorus compounds may include phosphoric anhydride (P2O5), polyphosphoric acid, orthophosphoric acid, phosphorus oxytrichloride (POCl3), phosphorus trichloride (PCl3), and thionating agents (P2S5). The mixture may contain from about 0.1 to about 10% by weight of the phosphorus compound, and asphalt compositions containing from 0.1 to 30% by weight of the polymer/phosphorus compound blend (modifier composition) may be prepared. It is believed that the inorganic phosphorus compound functions as a crosslinking agent between the rubber-base and/or resin-base modifier, and a higher order network structure (asphaltene) in the asphalt, and is useful to strengthen the gel structure in the asphalt.